The present invention relates to article holders that use gas vortices to hold an article in a desired position.
U.S. Pat. No. 6,168,697 issued Jan. 2, 2001 to Siniaguine et al., describes a wafer holder which emits gas vortices to hold a semiconductor wafer in a desired position while the wafer is etched with a plasma etch. The vortices have low pressure zones that hold the wafer proximate to the holder. In addition, the vortices cool the wafer. Unfortunately, the wafer cooling is not uniform. Portions of the wafer near the vortex outlets are cooled more than the rest of the wafer. The non-uniform cooling may have a negative effect on the etch uniformity, the etch rate being higher where the wafer is hotter.